In this study, the Pinus elliottii plantation in Wanling Forest Farm, Xuancheng City, Anhui Province was selected as the research object. A controlled field nitrogen (N) and phosphorus (P) addition experiment was conducted with five treatments, including control check (CK, N 0 kg/(hm²·a)+P 0 kg/(hm²·a)), low N (LN, N 50 kg/(hm²·a)+P 0 kg/(hm²·a)), high N (HN, N 100 kg/(hm²·a)+P 0 kg/(hm²·a)), high N and low P (HNLP, N 100 kg/(hm²·a)+P 50 kg/(hm²·a)) and high N and high P (HNHP, N 100 kg/(hm²·a)+P 100 kg/(hm²·a)). Based on five consecutive years of controlled experiments with N and P additions, basic soil properties, organic carbon fractions and hydrolytic enzyme activities of 0-20 cm and 20-40 cm soil layers were measured in 2023, to explore the effects of short-term N and P addition on soil organic carbon(SOC) fraction contents and their key influencing factors. The results showed that: 1) The addition of N and P significantly decreased soil pH by 3.49%-11.48%, and HNLP significantly increased the contents of NO- 3-N and total P respectively by 128.10% and 76.67%. 2) N addition of 5 years had no significant effect on the contents of SOC, particulate organic carbon(POC), mineral-associated organic carbon(MAOC) and microbial biomass carbon(MBC), while HN significantly increased the content of dissolved organic carbon(DOC). HNLP significantly increased the contents of SOC, POC and MAOC in 0-20 cm soil layer by 31.51%, 18.01%, and 27.12%, respectively, and significantly increased the content of MBC in 20-40 cm soil layer by 13.35%. 3) Structural equation model analysis showed that N and P addition changed the contents of NO- 3-N and total P in soil, affected soil carbon fractions by directly or indirectly affecting soil β-1,4-glucosidase, cellobisidase, β-1, 4-N-acetylglucosaminidase activities. Thus, from the perspective of long-term carbon sequestration, the mixed use of high N and low P is more beneficial to improve the stability of soil organic carbon, which provides theoretical support for forest management to realize the goals of forest carbon peaking and carbon neutrality.